Alexandra, from Claudy in Co Londonderry, was diagnosed at the age of 11 and given just three months to live, but defied the odds.

Rev Millar, a family friend who officiated at the Mass alongside parish priest Fr Chris Ferguson, told mourners at St Columb's Church in Londonderry that the teenager had "walked through ferocious storms" on her journey with cancer, but that her determination was "inspirational".

"Many who have gathered here today, and many more who are watching the service online throughout the world, will have been inspired by Alexandra," he said. "Alexandra our superstar, Alexandra our hero, Alexandra our princess, Alexandra our saint. But let's not forget, to her parents she was their beautiful child.

"But I guess at times a saint would have been the last word you would have used to describe her. Because like every other teenager she had her moods, her tantrums and fell out with her parents.

"It was only a few days ago when the family where going out to celebrate her birthday, and they had the table booked for 7.30pm, and guess who was sitting doing their make-up at 7.30pm. No, it wasn't her Daddy. It was Alexandra."

Alexandra fought Ewing's Sarcoma, a rare type of cancer that affects bones or the tissue around bones.

She died last Thursday in the Royal Belfast Hospital for Sick Children, surrounded by her family.

Rev Millar added: "Alexandra was no different from any other teenager, with her hopes and her dreams, with a future that lay before her, with her worries and her fears.

"There were days when she walked on the clouds and there were days she had to walk through the most ferocious storms and the darkest valleys.

"It makes me smile when I think of that determined young woman who embraced life, who faced those storms and fears head-on.

"She persevered through pain, she overcame great hurdles, she defied medical prognosis and yet she remained faithful to God.

"I will always remember that beautiful, cheeky smile, whether at the Royal or at home, that twinkle in her eyes as she chatted."

Rev Millar said the young girl was an inspiration to everyone.

He added: "And so as we face a future without Alexandra's presence in our lives, we are thankful to God that her love remains alive within each and every one of us. That her memories will not only give courage but also inspire us. And as we rebuild our lives, I would encourage you to follow her example."

Hundreds of bikers from all over Ireland provided a guard of honour, accompanying the teenager's coffin safely from her Claudy home to her Requiem Mass in Londonderry.

Leather-clad bikers, each carrying their helmets and with pink ribbons tied around their arms, mingled with mourners inside the church.

Many mourners, including Alexandra's friends from St Cecilia's and St Patrick's and St Brigid's Colleges wore yellow ribbons in their hair or on their lapels to represent Ewings Sarcoma, the disease Alexandra fought so bravely against.

Alexandra is survived by her parents Andre and Karen, sisters Danica and Carly, and brothers Ryan and Callum.

Ahead of the funeral, her heartbroken father Andre posted a moving tribute on the Facebook page where the family shared Alexandra's brave journey which touched the hearts of people around the world.

He said: "Today is going to be the hardest day of our lives but the strength our little angel showed us all during her short life will get us all through.

"We will never let our baby girl be forgotten and her name will live on forever as was her wish.

"Alexandra was an angel long before she was born and she is leaving this world a saint.

"Our hearts will never be the same again but you will keep them all strong with the memories you gave us and the impact you made on the world .

"Today is not goodbye but see you later Baby Girl. We got this."

During her treatment, Alexandra became a huge fan of the TV series Sons Of Anarchy. At the beginning of last year she got to meet her hero from the TV series, Opie played by Ryan Hurst.

The family were invited to meet the star at the Comic Con event in Wales and kept in touch afterwards.

Several gifts were brought to the altar during Sunday's service including a biker's helmet and a framed photo of her television hero Ryan Hurst.

He was among those who had paid tribute to the teenager online after her death.

He wrote: "Travel with love YaYa. May you be free to live shining among the stars."